Not a fan of protoframes, even as a one-off for 1999. That said, if they absolutely HAD to have been made, they make more sense as a one time thing. The continuous implementation of protoframes in new content is corrosive to game's tone and identity. The dating is also dreck.
Warframe 1999 should have been its own game.
Not only to not give Warframes pretty human faces (imo, a mistake) but also so that DE could've fleshed out the very interesting world you get pulled into.
But of course, the main concern would be that it wouldn't be profitable.